To prepare aromatic carbonyl compounds which are intended to be used as flavorings or fragrances, it is possible to utilize the oxidative cleavage of styrenes. For the preparation of vanillin, the oxidative cleavage of eugenol or isoeugenol with K.sub.2 Cr.sub.2 O.sub.7 /H.sub.2 SO.sub.4 has been described. In industry, vanillin is prepared predominantly by the alkaline hydrolysis of lignin (spent sulphite liquor from the paper industry) and oxidative cleavage of the resulting coniferyl alcohol (Rompp Lexikon Chemie, Version 1.5).
However, the aromatic carbonyl compounds prepared in this manner, such as, for example, vanillin, have the disadvantage that they are not permitted to be referred to as natural flavorings but only as nature-identical flavorings within the meaning of Directive 88/388/EEC on flavorings. Only compounds which have been prepared by physical processes (e.g., distillation or extraction) or biotechnological processes (enzymatically or microbially) can be referred to as natural flavorings.
To prepare natural benzaldehyde, for example, cassia oil is treated with hot steam.
EP-A 542,348 describes a process for the preparation of natural phenylaldehydes using the enzyme lipoxidase. If the substrates used are eugenol or isoeugenol, the reaction with the lipoxidase gives vanillin. Disadvantages of this process are the low conversions of from 0.3 to 15%.
DE-A 19,649,655 describes a process for the preparation of vanillin from ferulic acid in the presence of the enzyme ferulic acid deacylase. However, the enzyme can only be used for the preparation of vanillin starting from ferulic acid. Other starting materials are not suitable.
U.S. Pat. No. 5,128,253 describes the preparation of natural vanillin from ferulic acid or eugenol by biotransformation. Microorganisms used are Aspergillus niger, Rhodotorula glutinis and Corynebacterium glutamicum. The main disadvantage in this preparation is the long incubation time of, on average, from 7 to 10 days.
EP-A 405,197 describes the preparation of natural vanillin by oxidation of eugenol or isoeugenol using microorganisms of the genera Serratia, Klebsiella or Enterobacter. Within short reaction times, this method too, permits only relatively low yields.